The primary aim of this project will be continued study of the allograft problem. Studies of factors influencing transplant survival will utilize an extensive data base collected over the past 12 years and analyses will be done using an on-site computer facility. Factors to be examined include HLA-DR histocompatibility matching, possible enhancing antibodies, and the transfusion effect. Efforts will be made to devise means by which enhancing antibodies induced by transfusiuons can be detected. Sera from patients who subsequently reject grafts will be compared to those with successful grafts. Antimmunoglobulin antibodies are the principal antibodies postulated to be enhancing antibodies.